This application claims priority to Korean Patent Application No. 2003-0085768, filed on Nov. 28, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to data storage devices such as a hard disc drive, and more particularly, to an apparatus and method for limiting a speed of a head within the data storage device during unlatching with guarantee of unlatching regardless of a latch force.
2. Description of the Related Art
A hard disc drive (HDD) is an apparatus for magnetically writing/reading data on/from a rotating magnetic disc. The hard disc drive, which accesses bulk data at high speed, is widely used as an auxiliary memory device of a computer system.
A latch system of the hard disc drive prevents a disc and a head from being physically damaged from an external force when the hard disc drive is not operating. Such a latch system may be implemented with a magnetic mechanism, an electromagnetic mechanism, or a ramp loading mechanism. However, the magnetic mechanism is mainly used because of its relative simplicity. In the magnetic mechanism for the latch system, the position of the head is latched to a parking zone by a magnetic force of a magnetic latch located on the outside of a head assembly.
When the hard disc drive begins to operate, the head that is initially within the parking zone is moved onto a data zone of the disc. Such movement of the head is termed an “unlatch operation”.
The unlatch operation includes an acceleration time zone during which an acceleration current is input to a voice coil motor (VCM) to generate a torque on the head. Such a torque on the head overcomes a magnetic force of the magnetic latch. The unlatch operation also includes a brake time zone during which the head is stopped from accelerating after the head has already moved out from the parking zone.
The magnetic force used to latch the head to the parking zone varies widely among hard disc drives. In the prior art, for addressing such a variation, a magnitude and a time period of application of an acceleration current is determined for a greatest magnetic force to guarantee unlatching of the head for any hard disc drive.
Unfortunately, such prior art magnitude and time period of application of the acceleration current results in disadvantages. For example, in a hard disc drive with relatively lower magnetic force, the resulting moving speed of the head is excessively high. Such high moving speed of the head causes instability of a flying height of the head which may result in the head contacting the disc. Such contact detrimentally results in a scratch being generated on the surface of the disc.
In addition, with instability of the flying height of the head, servo information recorded on the disc is difficult to read with the head. Such servo information includes a servo sync mark, a track number, and a sector number, which are recorded in a servo sector. In order to stably read such servo information, the moving speed of the head is desired to be limited to be below a maximum moving speed.
However, in the prior art unlatch operation, an acceleration current with same magnitude and time period of application is used for any hard disc drive. Because the magnetic forces of the magnetic latches within hard disc drives vary, the moving speed of the head correspondingly varies and is not limited in the prior art unlatch operation.